Sensor system for a vacuum brake booster

ABSTRACT

The invention relates to a sensor arrangement ( 10 ) for a vacuum brake booster with a brake booster housing comprising at least one vacuum chamber ( 54 ) and one working chamber ( 26 ), which is separated from the latter by a moveable wall ( 20 ) and is connectable either to vacuum or at least atmospheric pressure, as well as a bore ( 18 ) disposed in the brake booster housing. The sensor arrangement ( 10 ) comprises a first partition ( 38 ), which seals the brake booster housing off from the ambient atmosphere when the sensor arrangement ( 10 ) is assembled. The sensor arrangement ( 10 ) also comprises a housing ( 12 ) with a first housing portion ( 13 ) which projects into the brake booster housing. The first housing portion ( 13 ) is divided by a second partition ( 40 ) into a first chamber ( 44 ) and a second chamber ( 46 ). When the sensor arrangement ( 10 ) is assembled the first housing portion ( 13 ) extends into the brake booster housing to an extent such that the first chamber ( 44 ) is directly connected to the vacuum chamber ( 54 ) of the brake booster via a first pressure inlet opening ( 52 ) and the second chamber ( 46 ) is directly connected to the working chamber ( 26 ) of the brake booster via a second pressure inlet opening ( 56 ). At least one pressure sensor ( 48, 50, 70 ) is disposed in the first housing portion ( 13 ).

[0001] The invention relates to a sensor arrangement for a vacuum brake booster for determining the pressure conditions prevailing in a brake booster and a vacuum brake booster provided with a sensor arrangement of this kind.

[0002] Information on the pressure conditions in a vacuum brake booster can be used in various ways. For example, the maximum output operating state of the brake booster, i.e. the state as from which the brake booster is no longer able to assist a further pressure increase, can be detected by sensing the pressure states in the brake booster. Furthermore, sensing of the level of the vacuum in a vacuum chamber of the brake booster may serve, for example, to control a vacuum pump creating the vacuum.

[0003] It is of particular advantage to sense the pressure states in a brake booster which is provided with an electromagnetic actuating unit. An electromagnetic actuating unit of this kind enables the vehicle brake system to be actuated by activating the brake booster in addition or as an alternative to pedal force-proportional actuation by the driver. For example, the above-mentioned electromagnetic actuating unit affords the possibility of operating the brake booster at maximum output independently of the pedal actuating force applied by the driver in a critical driving situation, e.g. when emergency braking, and thus providing the maximum possible braking force assistance (so-called brake assistant function). The pressure build-up speed in the working chamber of a brake booster can be used to recognize when a braking action is an emergency braking action. Knowledge of the pressure conditions in the brake booster is also of advantage when braking takes place completely automatically, for example in co-operation with a distance control system.

[0004] It is usual, for the purpose of measuring the pressure in a vacuum brake booster, to use pressure sensors whose signals are processed by a controller, as a rule electronic, in order to control the electromagnetic actuating unit as desired.

[0005] DE 44 36 297 A1 discloses a vacuum brake booster in which a pressure sensor for sensing the pressure in a working chamber is rigidly connected to a moveable wall disposed between a vacuum chamber and a working chamber. The pressure in the vacuum chamber is measured by a second pressure sensor, which is disposed either outside of a brake booster housing or inside the vacuum chamber.

[0006] U.S. Pat. No. 4,633,757 discloses a vacuum brake booster with a pressure sensor disposed in a working chamber and a pressure sensor disposed in a vacuum chamber, wherein the pressure sensors are each secured to an inner wall of the brake booster housing. The disadvantage of these known arrangements lies in the fact that assembly and inspection and any necessary replacement of the pressure sensor give rise to significant difficulties and entail considerable expenditure.

[0007] DE 197 29 158 C1 describes a vacuum brake booster with a pressure sensor which is disposed in a housing that is externally flange-mounted on a brake booster housing. The pressure sensor is connected to at least one working chamber and at least one is vacuum chamber via air guide ducts, which extend from the housing of the sensor arrangement into the brake booster housing. However the space requirements are increased as a result of disposing the pressure sensor outside of the brake booster housing.

[0008] The object of the invention is to provide a sensor arrangement for sensing the pressure conditions in a vacuum brake booster which is structured in the simplest and most space-saving manner possible, although is at the same time easy to assembly and maintain.

[0009] This object is achieved according to the invention by a sensor arrangement having the features indicated in claim 1. The sensor arrangement according to the invention is distinguished by the fact that at least one pressure sensor is disposed in a space-saving manner in a first housing portion which projects through a bore formed in a brake booster housing into the interior of the brake booster housing when the sensor arrangement is assembled. A first partition seals the brake booster housing off from the ambient atmosphere when the sensor arrangement is assembled. The first housing portion is divided by means of a second partition into a first chamber and a second chamber and extends into the brake booster housing to an extent such that the first chamber is connected to the vacuum chamber of the of the brake booster via a first pressure inlet opening and the second chamber is connected to the working chamber of the brake booster via a second pressure inlet opening. It is not necessary to attach special holders for the, at least one, pressure sensor, nor to configure the brake booster housing in a special way, which means that rational series production of different brake boosters with the same type of housing is possible. It is also unnecessary to modify the booster geometry. The solution according to the invention also has the advantage of the, at least one, pressure sensor being disposed in the interior of the brake booster housing and connected directly to the working chamber and the vacuum chamber of the brake booster via the pressure inlet openings, which increases accuracy of measurement and reduces susceptibility to errors.

[0010] In a preferred embodiment of the sensor arrangement according to the invention a pressure sensor is disposed in each of the two chambers of the first housing portion, one of which pressure sensors senses the pressure in the vacuum chamber and the other the pressure in the working chamber.

[0011] The pressure sensors are preferably absolute pressure sensors which sense the absolute pressure in the vacuum chamber and the working chamber. According to one embodiment of the sensor arrangement according to the invention, the first partition and the second partition constitute part of a one-piece housing insert which is disposed in the first housing portion. A configuration of this kind enables the sensor arrangement to be manufactured economically, as the housing insert can be manufactured at a low cost, e.g. as a plastics injection-molded part.

[0012] The first housing portion is preferably of a hollow cylindrical form. The first partition and the second partition are advantageously of a diameter which is smaller than the inside diameter of the first housing portion, and a sealing element, in particular an O-ring, is disposed between each partition and an inner wall of the first housing portion. Thus the first housing portion is sealed off from the ambient atmosphere and the two chambers are separated in a sealing fashion at low cost, as commercially available O-rings can be used.

[0013] According to a further embodiment of the sensor arrangement according to the invention, a pressure sensor formed as a differential pressure sensor is disposed just in one of the two chambers of the first housing portion. This differential pressure sensor, which is the sole pressure sensor of this embodiment, is connected to the first chamber via a third pressure inlet opening and to the second chamber of the first housing portion via a fourth pressure inlet opening. A sensor arrangement configured in this way, connected to a controller, is capable, by means of the differential pressure sensor, to detect the pressure difference in each case operating at the moveable wall of the brake booster and determine from this the power-assisted braking which is actually operative.

[0014] According to a preferred configuration of the sensor arrangement according to the invention, the second partition is formed by an outer portion of the differential pressure sensor which is sealingly connected to an inner wall of the first housing portion. A configuration of this kind is particularly simple and inexpensive, as the second partition does not have to be constructed as a separate component.

[0015] The first partition is preferably sealingly connected to an inner wall of a second housing portion disposed outside of the brake booster housing. This arrangement enables the sensor arrangement to be preassembled in the housing and then fitted in the bore formed in the brake booster housing in one operation.

[0016] According to an advantageous configuration of the sensor arrangement according to the invention, the, at least one, pressure sensor is electrically connected via at least one connecting line which is passed through the first partition or the partitions in a sealed fashion. This, at least one, connecting line may be led outside of the brake booster housing to any desired connection point, for example to an electronic controller.

[0017] According to a further embodiment of the sensor arrangement according to the invention, at least one carrier element for the, at least one, pressure sensor consists of electrically conductive material and is passed in sealed fashion through the first partition or the partitions. There is no need to provide the above-mentioned electrical connecting line in this arrangement.

[0018] The, at least one, connecting line is preferably led to a connector disposed outside of the brake booster housing. The connector disposed outside of the brake booster housing may also be directly connected to the carrier element consisting of electrically conductive material. A configuration of this kind enables the pressure sensor to be preassembled in the brake booster housing, while its electrical connection, for example to an electronic controller, can be established when installing the brake booster by simply connecting the connector.

[0019] According to a further embodiment of the sensor arrangement according to the invention, the first partition is part of a housing of an electronic controller, in which an electronic printed circuit board is disposed, this being connected in an electrically conductive manner to the, at least one, pressure sensor. The electronic printed circuit board can be connected to the, at least one, pressure sensor either via the, at least one, connecting line or the, at least one, carrier element consisting of electrically conductive material. This embodiment of the invention is distinguished by the fact that the, at least one, pressure sensor can be preassembled with the electronic controller to form a subassembly. The direct flange-mounting of the controller on the brake booster housing facilitates assembly and saves space. It also enables the connection paths of the electrical lines to be short and thus less susceptible to interference.

[0020] A brake booster provided with the sensor arrangement according to the invention can be manufactured at low cost, as the sensor arrangement can be positioned in the interior of the brake booster housing in a simple assembly process without having to modify the brake booster housing or the brake booster geometry in a particular way. Not only is the arrangement of the, at least one, pressure sensor in the interior of the brake booster housing a particularly space-saving measure, but it also enables the pressure conditions in the brake booster to be sensed particularly reliably.

[0021] Several embodiments of a sensor arrangement according to the invention are illustrated in detail in the following on the basis of the accompanying schematic figures, in which:

[0022]FIG. 1 is a sectional side view of a first embodiment of the sensor arrangement according to the invention in the assembled state,

[0023]FIG. 2 is a sectional side view of another embodiment of the sensor arrangement according to the invention in the assembled state.

[0024] The sensor arrangement 10 represented in FIG. 1 comprises a one-piece housing 12 with a hollow cylindrical first housing portion 13 and a second housing portion 14 adjoining the latter. When the sensor arrangement 10 is assembled, the second housing portion 14 is disposed outside of a brake booster housing, which is not represented in its entirety here, while the first housing portion 13 projects through a first bore 18 formed in a housing wall 16 of a vacuum brake booster, a second bore 22 formed in a moveable wall 20, and a third bore 28 formed in a boundary wall 24 of a working chamber 26 into the interior of the brake booster housing. Pressure-tight sealing is effected by respective sealing elements 30, 32 34 which are inserted in the region of the bores 18, 22, 28 and through which the first housing portion 13 is passed.

[0025] A housing insert 36, which is constructed as a one-piece component with a first partition 38 and a second partition 40, for example as a plastics injection-molded part, is disposed in the interior of the first housing portion 13. The first partition 38 is sealingly connected to an inner wall 42 of the first housing portion 13 to provide a seal against the ambient atmosphere. The other partition 40 is likewise sealingly connected to the inner wall 42 of the first housing portion 13 and divides the first housing portion 13 into a first chamber 44 and a second chamber 46. The first partition 38 and the second partition 40 are of a diameter which is smaller than the inside diameter of the hollow cylindrical first housing portion 13, so that sealing elements 47 a, 47 b are disposed between each partition 38, 40 and the inner wall 42 of the first housing portion 13 to provide the sealing connection. The dimensions of the partitions 38, 40 and the first housing portion 13 are selected such that commercially available O-rings can be used as sealing elements 47 a, 47 b.

[0026] A pressure sensor 48, 50 constructed as an absolute pressure sensor is disposed in each of the two chambers 44, 46. The first chamber 44 is connected to a vacuum chamber 54 of the vacuum brake booster via a first pressure inlet opening, so that the pressure sensor 48 positioned in the first chamber 44 senses the pressure in the vacuum chamber 54. The second chamber 46 is connected to the working chamber 26 of the vacuum brake booster via a second pressure inlet opening 56, so that the pressure sensor 50 positioned in the second chamber 46 senses the pressure in the working chamber 26.

[0027] The pressure sensor 48 positioned in the first chamber 44 is disposed on a carrier element 58 which consists of an electrically conductive material and is led in sealed fashion through the first partition 38 into the second portion 14 of the housing 12. The pressure sensor 50 positioned in the second chamber 46 is disposed on a carrier element 60 which likewise consists of an electrically conductive material. The carrier element 60 is passed in sealed fashion through the second partition 40 and the first partition 38 into the second portion 14 of the housing 12. The carrier elements 58, 60 are connected to an electrical connector 62 in the second portion 14 of the housing 12.

[0028] The pressure sensors 48, 50 comprise electrical connections 64 on two opposite sides. The electrical connections 64 of the pressure sensors 48, 50 are soldered or welded to the respective carrier element 58, 60, so that the pressure sensors 48, 50 are mechanically fixed to the respective carrier element 58, 60.

[0029] Another embodiment of the sensor arrangement 10 in the assembled state is reproduced in FIG. 2. The first partition 38 is sealingly connected to an inner wall 66 of the second housing portion 14 to provide a seal against the ambient atmosphere. The first partition 38 is of a diameter which is smaller than the inside diameter of the hollow cylindrical second housing portion 14, so that the sealing element 47 a is disposed between the partition 38 and the inner wall 66 of the second housing portion 14 to provide a seal.

[0030] A pressure sensor 70 which is formed as a differential pressure sensor is disposed in the first chamber 44. The pressure sensor 70 comprises a cylindrical centre portion 72 which is adjoined at its two end sides by respective outer portions 74 a, 74 b. The diameter of the outer portions 74 a, 74 b is greater in a region adjacent to the centre portion 72 than the diameter of the center portion 72. Cooperating with the sealing element 47 b, the outer portion 74 b of the pressure sensor 70, which is directed into the interior of the brake booster housing, forms the second partition 40. The sealing element 47 b is disposed in a region of the center portion 72 of the pressure sensor 70 which is adjacent to the outer portion 74 b between the portion 72 and the inner wall 42 of the first housing portion 13, so that the widened diameter of the outer portion 74 b, in cooperation with the sealing element 47 b, limits the axial displaceability of the pressure sensor 70 along a longitudinal axis L.

[0031] A third pressure inlet opening 76 formed in the pressure sensor 70 connects the pressure sensor 70 to the first chamber 44, the pressure in which corresponds to the pressure in the vacuum chamber 54. A fourth pressure inlet opening, which is formed at the opposite side of the pressure sensor 70 and is not represented in the figure, connects the pressure sensor 70 to the second chamber 46, the pressure in which corresponds to the pressure in the working chamber 26. The differential pressure sensor 70 can thus sense the pressure difference between the vacuum chamber 54 and the working chamber 26.

[0032] The pressure sensor 70 is electrically connected by connecting lines 78, which are passed in sealed fashion through the first partition 38 and connected to the electrical connector 62.

[0033] According to a further embodiment, which is not represented here, an electronic controller is flange-mounted directly on the housing wall 16 of the brake booster in sealing fashion by means of a sealing element. The first partition 38, which separates the interior space of the brake booster housing from the ambient atmosphere, is formed by a region of a controller housing. The controller comprises an electronic printed circuit board, which is connected in an electrically conductive manner via the connecting lines 78 or the electrically conductive carrier elements 58, 60 directly to the electrical connections 64 of the absolute pressure sensors 48, 50 or the differential pressure sensor 70. 

1. Sensor arrangement (10) for a vacuum brake booster comprising a brake booster housing with at least one vacuum chamber (54) and one working chamber (26), which is separated from the latter by a moveable wall (20) and is connectable either to vacuum or at least atmospheric pressure, as well as a bore (18) disposed in the brake booster housing, wherein the sensor arrangement (10) comprises: a first partition (38), which seals the brake booster housing off from the ambient atmosphere when the sensor arrangement (10) is assembled, a housing (12) with a first housing portion (13) which projects into the brake booster housing and is divided by a second partition (40) into a first chamber (44) and a second chamber (46), wherein, when the sensor arrangement (10) is assembled, the first housing portion (13) extends into the brake booster housing to an extent such that the first chamber (44) is directly connected to the vacuum chamber (54) of the brake booster via a first pressure inlet opening (52) and the second chamber (46) is directly connected to the working chamber (26) of the brake booster via a second pressure inlet opening (56), and at least one pressure sensor (48, 50, 70) disposed in the first housing portion (13).
 2. Sensor arrangement according to claim 1, characterized in that a pressure sensor (48, 50) is disposed in each of the two chambers (44, 46) of the first housing portion (13).
 3. Sensor arrangement according to claim 2, characterized in that the pressure sensors (48, 50) are absolute pressure sensors.
 4. Sensor arrangement according to one of the preceding Claims, characterized in that the first partition (38) and the second partition (40) constitute part of a one-piece housing insert (36) which is disposed in the first housing portion (13).
 5. Sensor arrangement according to one of the preceding Claims, characterized in that the first housing portion (13) is of a hollow cylindrical form.
 6. Sensor arrangement according to claim 5, characterized in that the first partition (38) and the second partition (40) are of a diameter which is smaller than the inside diameter of the first housing portion (13), and a sealing element (47 a, 47 b), in particular an O-ring, is disposed between each partition (38, 40) and an inner wall (42) of the first housing portion (13).
 7. Sensor arrangement according to claim 1, characterized in that a pressure sensor (70) formed as a differential pressure sensor is disposed just in one of the two chambers (44, 46) of the first housing portion (13) and is connected to the first chamber (44) of the first housing portion (13) via a third pressure inlet opening (76) and to the second chamber (46) of the first housing portion (13) via a fourth pressure inlet opening (78).
 8. Sensor arrangement according to claim 7, characterized in that the second partition (40) is formed by an outer portion (74 b) of the differential pressure sensor (70) which is sealingly connected to an inner wall (42) of the first housing portion (13).
 9. Sensor arrangement according to one of claims 1 to 3 or 5 to 8, characterized in that the first partition (38) is sealingly connected to an inner wall (66) of a second housing portion (14) disposed outside of the brake booster housing.
 10. Sensor arrangement according to one of the preceding Claims, characterized in that the, at least one, pressure sensor (48, 50, 70) is electrically connected via at least one connecting line (78) which is passed through the first partition (38) or the partitions (38, 40) in a sealed fashion.
 11. Sensor arrangement according to one of claims 1 to 9, characterized in that at least one carrier element (58, 60) for the, at least one, pressure sensor (48, 50, 70) consists of electrically conductive material and is passed through the first partition (38) or the partitions (38, 40) in sealed fashion.
 12. Sensor arrangement according to claim 10, characterized in that the, at least one, connecting line (78) is led to a connector (62) disposed outside of the brake booster housing.
 13. Sensor arrangement according to claim 11, characterized in that the, at least one, carrier element (58, 60) is led to a connector (62) disposed outside of the brake booster housing.
 14. Sensor arrangement according to one of claims 1 to 3, 5, 7 or 9 to 13, characterized in that the first partition (38) is part of a housing of an electronic controller, in which an electronic printed circuit board is disposed, this being connected in electrically conductive manner to the, at least one, pressure sensor (48, 50, 70).
 15. Vacuum brake booster with a brake booster housing containing at least one vacuum chamber (54) and one working chamber (26), which is separated from the latter by a moveable wall (20) and is connectable either to vacuum or at least atmospheric pressure, characterized by a sensor arrangement (10) according to one of claims 1 to
 14. 